| Summary: | 碩士 === 國立中興大學 === 植物學系 === 84 === The aim of this study was to elucidate the effects of the
different root temperatures (35, 25, 15 degree )on growth and
nitrogen metabolism of muskmelon (Cucummis melo L.) under the
hydroponic system. Examinations on the changes of the
physiological characterics under different root temperatures
including biomass, photosynthetic rate, respiration rate,
stomatal conductance, content of free amino acid, soluble, and
the enzyme activities of NR, NiR, GS, GOGAT,GDH, and Rubisco.
The results were summarized as follows: The decreasing of
root temperature resulted in the decreasing of photo-synthetic
rate, respiration rate, Rubisco activity and total dry weight in
leaves. The lowest root temperature inhibited the absorpting of
nutrition onplant growth. Undeer 15 degree root temperature
treatment, the content of total solubleprotein was lowest in
both roots and leaves. Furthermore, the activities ofNR and NiR
were lowest in root, but highest in leaves. The reason may be an
increasing in the flow rate of nitrate into leaves. Therefore,
the assimilation of nitrogen increasing in leaves on low
temperature. In higher plants, ammonina is mainly assimilated by
GS and GOGAT pathway which produces glutamine andglutamate. The
low temperature inhibited GS/GOGAT activities in roots.
Thereforethat is favorable to ammonium assimilation in leaves.
Our results showed that indeed asparagine was the highest
content among 20amino acids in leaves and roots of all root
temperature treatments. In fruit growth period, the transmitting
of asparagine is very important from leaves and roots. For this
reason, changes in amino acids content and composition of sink
(fruit) was more important than the effect of root temperature.
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